Reverse circulation pellet impact drilling and coring apparatus



Sept 13, 1955 w. EDGERwooD, .1R 2,717,761

REVERSE CIRCULATION PELLET IMPACT DRILLING AND CORING APPARATUS Filed Jan. 29, 1952 P' Lerozs UfLedSerzB'ood Jr. Erm/amber REVERSE CHRCULATIN PELLET IMIPACT DRILLlNG AND COG APPARATUS Okla., assigner to Esso Leroy W. Ledgerwood, Jr., Tulsa,

a corporation of Research and Engineering Company, Delaware Application January 29, 1952, Serial No. 268,881 7 Claims. (Cl. Z55-1.8)

This invention concerns an improved form of drill bit employing the multitudinous forceful impact of pellets to secure a drilling action. The invention particularly concerns a form of drill bit in which a number of nozzle elements are annularly arranged in and pass through a drill head which is supported on a drill pipe or other tubular member. By passage of lluid downwardly through the annular space between the drill pipe and the bore hole, fluid is ejected through the annular nozzles. Recirculation means are included for the continuous circulation of pellets through these nozzles to secure a pellet drilling aeition. Return circulation of the drilling lluid is through the inside of the drill string. The pulverizing pattern of the pellets may be adapted for the cutting of cores which may be brought to the surface of the earth through the drill string in the return llow of drilling lluid.

The basic principles of pellet impact drilling are fundamentally simple. Means are simply required to provide a jet of high velocity lluid including provision for entraining and accelerating pellets in this jet of lluid. The requisites of this drilling procedure concern the nature of the pellets employed, and the lluid employed therewith as a propelling and recirculation agent for the pellets.

The pellets to be employed must be of substantial size. Thus it has been found that granular pellets or pellets having a diameter less than 1/8 of an inch are relatively ineffective in drilling. In general the rate of drilling attainable increases as the size ofthe pellets is increased. For this reason it is generally preferred to employ the largest pellets possible, consistent with the nozzle size of the apparatus and the fracturing characteristics of the pellets. As will be emphasized, the nature of the drilling lluid employed also has a bearing on the size of the pellets. However, it Amay be stated that when employing a gas, such as air, for the drilling lluid, pellets of about 1A to a quarter of an inch iu diameter are to be employed. When using a liquid, such as water or drilling mud, as the drilling lluid, the pellets may range in size from about 1A to l inch.

lt is important that the pellets have the greatest practical density. It is apparent that the greater the density of a given sized pellet the greater the kinetic energy which can be attained and the greater the impact force which can be developed. Again, as will be brought out, the separation characteristics of the pellets from the drilling fluid employed play an important part in drilling efciency. Since the separation rate of the pellets from a fluid depends in part upon the density of the pellets, it is apparent that this factor again dictates use of a high density pellet.

The configuration and surface characteristics of the pellets are also important. The pellets should be substantially spherical in nature and should have a smooth non-abrasive surface so as to limit wear of the jet nozzle assembly through which the pellets are to be ejected. `ln this connection it is fundamental that a spherical body s Patent Mice possesses the best resistance to fracture due to impact; no other shape possesses the mechanical strength of a sphere. The factors of spherical configuration and smooth surface also relate to the separation characteristics of the pellets from the entraining fluid as will be noted below.

In view of these considerations the pellets to be employed are generally metal spheres having the desired properties of impact resistance, hardness, and toughness. Iron, steel and other ferrous alloys may be employed to prepare the pellets. In this connection, however, it should be observed that it is essential that the metal chosen be non-brittle in character. Due to their high density, tungsten carbide alloys of the less brittle character are attractive for use in the pellets to be employed. Again, alloys of this character or other dense metals may be employed as a pellet core material, surfaced by ferrous alloys having the requisite toughness.

As suggested heretofore, the separation characteristics of the pellets from the drilling fluid play an important part in the elliciency of pellet impact drilling. It is apparent that in jetting a stream of lluid, entraining the pellets referred to, against a formation to be drilled, it becomes important that the pellets readily separate from this stream of lluid. This is required so that the pellets will not be cushioned by the fluid and will not be inefliciently swept from the drilling zone in the lluid flow stream. Again, regardless of the type of pellet recirculation employed, it becomes necessary in some manner to subsequently secure separation of pellets from an upward flow of drilling mud in the bore hole for return and recirculation of the pellets to the drilling zone.

Consequently, as emphasized heretofore, pellets of the character defined must be employed to have the separation characteristics required for effective drilling. ln this connection it is apparent that the nature of the drilling fluid employed also affects the separation characteristics of the pellets. From this viewpoint it is desirable to employ a drilling lluid having the lowest viscosity and lowest density practical, consistent with other requirements of the drilling fluid. It has been found, on the basis of drilling conducted heretofore, that the drilling rate obtainable is proportional to the ratio of the density of the pellets to the density of the drilling lluid. This consideration makes the use of air or other gas attractive. Similarly, if a liquid is to be employed, water or other low density liquid is preferably employed. Nonetheless, if considered desirable, drilling muds of the character conventionally used in rotary drilling may be employed.

Recirculation of the pellets in the immediate vicinity of the drilling zone may be accomplished in a number of ways. When the pellets have been forced against a formation by jetted lluid, the lluid llow will carry the pellets upwardly in the bore hole. At some point spaced above the bottom of the bore hole, it becomes necessary therefore toseparate the entrained pellets from the upllowing drilling lluid. One method by which this may be accomplished is to provide a low velocity lluid zone above the drilling apparatus in which the pellets may settle by gravity into a recirculation system. Such a low velocity zone may be established by providing an enlarged cross-sectional area for lluid ilow immediately above the drill. This gravity recirculation can be supplemented or substituted by a mechanical deflection system serving to maintain the pellets in captive recirculation. A shroud may be employed for this purpose of a character substantially blocking the return lluid llow path but containing passages through which drilling lluid and pulverized earth formation may be carried to the surface of the earth. This shroud would be essentially of the nature disclosed and claimed in co-pending application Ser. No.

3 268,882 of Leroy W. Ledgerwood, lr., filed January 29, 1952.

A suitable nozzle assembly is required to convert fluid pumping pressure to velocity energy. Fluid pumped through the nozzle is subjected to a substantial pressure drop to provide a constricted directed high velocity jet of fluid in which the pellets are entrained. The jet or jets of fluid together with the entrained pellets are then directed against the earth formation to be drilled.

The present invention concerns a particular modification of the basic principles of pellet impact drilling which have been described. The invention is particularly intended for reverse circulation in which drilling huid is passed downwardly in the annulus of a bore hole and upwardly from the drilling zone through the inside of a drill string. Reverse circuation drilling provides certain advantages over the conventional circulatory system. For example, by employing reverse circulation, return to the surface of pulverize'd earth and uid elux from formations encountered is facilitated. In addition, as will be disclosed herein, the present invention is adaptable to the cutting of a core which may be returned directly to the surface of the earth through the drill string by employing reverse circulation. The invention may be understood by reference to the accompanying drawing, in which:

Figure l shows a basic form of the drill bit of this invention in elevational view, partly in cross-section; and

Figure 2 is a cross-sectional view of the apparatus of Figure l along the line II-H.

As illustrated in the drawing, the drill of this invention is to be suitably attached to a drill string i. The drill string l is xed to an enlarged tubular member 13 which in turn is attached to an enlarged drill head member 2. Drill head 2 is provided with cutting or reaming means around the outer periphery of the drill head. Thus, for example, ilutes may be arranged on the lower periphery of the drill head. Again, if desired, hardened inserts or cutting teeth 3 may be provided along the lower external edge of the drill head 2. As will be disclosed, it is the function of these cutting means under the rotation of the drill head to enlarge the bore hole which is obtained by operation of the pellet impact drilling to be described. The cutting or rea-ming action of the drill head also serves to cut a constant diameter, gage size hole which tits snugly on drill head 2 to prevent ow of fluid between the drill head and the wall of the bore hole.

The enlarged drill head member 2 provides what may be considered anv upper shoulder 4 between tubular member 13 and the outer surfaceV of the drill head 2. Through this shoulder and through thev drillv head a number of narrow, constricted passages 5 may be cut. These passages serve as nozzle so that on pumping drilling fluid downwardly through the bore hole this fluid will be ejected through nozzle passages 5 to be expelled below the drill head in the form of iluid jets.

An enlarged central channel 7 is provided within the drill head 2. This channel preferably has the streamlined shape illustrated to facilitate return of drilling fluid upwardly through this channel. A sleeve member 8 is centrally positioned within the tubular member 13 and is fixed to the drill head 2. As shown, the sleeve member 8 has the same internal diameter as the upward termination of channel 7 in drill head 2. The sleeve member is employed to maintain an annular channel about the sleeve' 8 and within tubular member 13. A number of outwardly inclined conduit passages 9 cannect nozzle element 5 with this annular space.

In the operation of the drill described, drilling fluid is pumped downwardly through a surface casing member into the annular space between the drill string 1 and the bore hole cut by the apparatus. This drilling fluid passes downwardly through the nozzle elements 5. By virtue of the constricted passageway provided by these nozzle elements, the iluid is ejected in the form of a high velocity directed jet of fluid below the drill head 2. Assuming that pellets are entrained in this drilling iluid, these pellets will be directed downwardly against the bottom of the bore hole with substantial force. The pellets will cut the general drilling pattern illustrated in the drawing. Carried by the fluid the pellets will be forced along the bottom of the bore hole and upwardly through the central channel 7 and through sleeve element 8. The passage provided through channel 7 and sleeve element 3 may be considered to be a constricted fluid passage of a nature to maintain high flow rates. The How rate is such as to maintain the pellets in suspension in the upllowing drilling fluid. However, immediately above the lip` of sleeve element 8 a substantially greater diameter channel is available within tubular member 13 for the passage of the drilling fluid. Consequently, as the uid passes above the sleeve 8, a lower velocity iluid zone is encountered. This low velocity zone serves as a separation zone for the pellets which are permitted and caused to settle from the upflowing drilling duid so as to drop in the annular space between sleeve 8 and tubular member 13. Here the pellets may drop downwardly through conduits 9 to obtain access to the nozzle elements 5. This recirculation of the pellets through the nozzles 5 is substantially aided by the aspiration force of the nozzles.

In order for the drill described to operate properly, it is essential that the drill head 2 provide a substantially fluid tight seal in the bore hole cut by the pellets. For this reason it is desirable that the drill head 2 be suflciently elongated so that any clearance between the drill head and the bore hole imposes a substantial pressure drop on luid which would otherwise tend to bypass the nozzle element 5. For this same purpose it is desirable that the drill head 2 be slightly tapered so that at all times the drill head is maintained in tight fitting relationship with the bore hole.

Utilizing relatively high rates of iluid flow, the pellets can be caused to cut the drilling pattern illustrated by the full lines in Figure 1. Thus the flow velocity may be sufficiently high to carry the pellets inwardly toward the axis of the bore hole so as to cut away the entire central portion of the bore hole. However, by using somewhat reduced rates of fluid flow, a cutting pattern of the nature indicated by the dashed lines may be obtained. In this case the fluid flow is suicient to secure eifective pellet impact drilling only immediately below the nozzle elements 5, and is not suicient to wear away the central portion of the bore hole by the fluid and solid erosion which occurs as the fluid ilows inwardly and upwardly through central channel 7 of the drill head. Consequently, as illustrated, a core element 11 of the formation is cut. This core element since it is centrally positioned in line with the passages through the apparatus may be carried upwardly by the stream of drilling huid to the surface of the earth. When the drill is used in this manner, it is preferable to position a wedge element within the lower termination of the drill string. Such wedge elements are conventional in coring bits. As the cutting action proceeds this wedge will contact the core 11 so as to break the core permitting segments of the core to be carried upwardly within the drill string. In this manner the drill illustrated may be employed as a core drill.

As illustrated, the nozzles 5 may be directed inwardly toward the axis of the bore hole at a slight inclination. The angle of inclination may be varied to establish a desired drilling pattern or to facilitate coring operations.

A particularly desirable use of the drill of this invention necessitates periodic changes in the rate and volume of fluid circulation. Normally sufficient iluid flow may be maintained to completely pulverize the central portion of the bore hole in the pattern shown by full lines. Periodically, however, fluid ow may be reduced so that 5 a central core remains as shown by the dashed lines. Resumption of normal fluid circulation will then cut the core free and force it to the surface of the earth through the drill string.

What is claimed is:

1. The method of drilling a bore hole in the earth comprising passing iluid downwardly in an annular channel between a hollow drilling element and, the wall of the bore hole, dividing said annular channel fluid How into a plurality of constricted, high velocity, uid streams, entraining a plurality of spherical pellets in each of said constricted fluid streams and directing said streams including the pellets against the bottom of the bore hole adjacent the wall thereof, passing said fluid and pellets upwardly in a central channel within said drilling element, separating said pellets from upwardly flowing fluid and re-entraining said pellets in said high velocity uid streams.

2. The method of claim l wherein said fluid and pellets are redirected upwardly from the bottom of the bore hole at a distance from the wall of the bore hole of less than the radius of the bore hole whereby a core is cut.

3. A device for drilling a bore hole in the earth cornprising a tubular member adapted to extend downwardly into a bore hole, said member terminating in a lower portion of appreciably greater external diameter than the upper portion thereof, said lower portion having a plurality of annularly arranged downwardly directed nozzles establishing fluid communication between the bore hole annulus adjacent said upper portion of said member and the bore hole below said member and a plurality of passageways within the said lower portion of said member, each of said passageways communicating between an intermediate section of one of said nozzles and the interior bore of said tubular member.

4. An apparatus for drilling bore holes in the earth comprising in combination: a tubular support member, an essentially cylindrical drill head member xed to the lower end of said support member, said drill head member being of larger external diameter than said support member and having a plurality of circumferentially arranged downwardly directed nozzle passageways providing fluid communication between points adjacent the lower external circumference of the drill head and points adjacent the upper external circumference of the drill head exterior of its juncture with said support member, said drill head member also having a central bore of small diameter than the bore of said support member, and an axially arranged sleeve supported by said drill head within said support member and defining with said support member an internal annular chamber, said drill head being provided with a plurality of conduit passages extending between said annular chamber and said nozzle passageways.

5. The apparatus dened by claim 4 in which the said drilling head includes cutting elements on the lower periphery thereof.

6. The apparatus defined by claim 4 in which the said nozzle passages are inclined toward the axis of the drilling head member.

7. The drill defined by claim 4 in which the said drill head constitutes a massive elongated member having a downward taper along at least a portion of the periphery thereof.

References Cited inthe file of this patent UNITED STATES PATENTS 649,488 Schrader May 15, 1900 1,071,199 Andrews Aug. 26, 1913 1,502,851 Gale July 29, 1924 1,669,098 Merritt May 8, 1928 2,233,260 Hawthorne Feb. 25, 1941 

